X-Ray Halo around the Spiral Galaxy NGC 4631 Observed with Suzaku

Yamasaki, Noriko Y.; Sato, Kosuke; Mitsuishi, Ikuyuki; Ohashi, T.

doi:10.1093/pasj/61.sp1.s291

Cited by 47 publications

(49 citation statements)

References 38 publications

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“…If the NPS and other prominent structures near the Fermi bubbles are all related by origin, the Galactic halo is important as a reservoir of thermal gas into which bubbles expand. Although nearby spiral galaxies sometimes exhibit a diffuse thermal X-ray halo that has kT ~ 0.1-0.6 keV and extends out ~10 kpc (e.g., [57,58]), the structural properties, temperature, and metallicity of the Galactic halo gas are not well constrained, which leads to differing observations. For example, Yoshino et al [59] performed a uniform analysis of the diffuse soft X-ray emission associated with the Galactic halo observed in 14 fields by Suzaku.…”

Section: Galactic Halomentioning

confidence: 99%

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

et al. 2018

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The Fermi bubbles were possibly created by large injections of energy into the Galactic Center (GC), either by an active galactic nucleus (AGN) or by nuclear starburst more than ~10 Myr ago. However, the origin of the diffuse gamma-ray emission associated with Loop I, a radio continuum loop spanning across 100° on the sky, is still being debated. The northern-most part of Loop I, known as the North Polar Spur (NPS), is the brightest arm and is even clearly visible in the ROSAT X-ray sky map. In this paper, we present a comprehensive review on the X-ray observations of the Fermi bubbles and their possible association with the NPS and Loop I structures. Using uniform analysis of archival Suzaku and Swift data, we show that X-ray plasma with kT~0.3 keV and low metal abundance (Z~0.2 Z◉) is ubiquitous in both the bubbles and Loop I and is naturally interpreted as weakly shock-heated Galactic halo gas. However, the observed asymmetry of the X-ray-emitting gas above and below the GC has still not been resolved; it cannot be fully explained by the inclination of the axis of the Fermi bubbles to the Galactic disk normal. We argue that the NPS and Loop I may be asymmetric remnants of a large explosion that occurred before the event that created the Fermi bubbles, and that the soft gamma-ray emission from Loop I may be due to either π0 decay of accelerated protons or electron bremsstrahlung.

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Section: Galactic Halomentioning

confidence: 99%

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

et al. 2018

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“…The out-of-galactic-plane outflow material emits strong continuum and line X-rays (Bregman et al 1995;Dahlem et al 1998;Wang et al 2001;Strickland et al 2004;Yamasaki et al 2009), implying that it contains substantial hot, thermal, ionised gases. The discovery of synchrotron emission halos associated with galactic outflows in some starburst galaxies, e.g.…”

Section: Introductionmentioning

confidence: 99%

Charge-exchange emission and cold clumps in multiphase galactic outflows

Owen

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Large-scale outflows from starburst galaxies are multi-phase, multi-component fluids. Charge-exchange lines which originate from the interfacing surface between the neutral and ionised components are a useful diagnostic of the cold dense structures in the galactic outflow. From the charge-exchange lines observed in the nearby starburst galaxy M82, we conduct surface-to-volume analyses and deduce that the cold dense clumps in its galactic outflow have flattened shapes, resembling a hamburger or a pancake morphology rather than elongated shapes. The observed filamentary Hα features are therefore not prime charge-exchange line emitters. They are stripped material torn from the slow moving dense clumps by the faster moving ionised fluid which are subsequently warmed and stretched into elongated shapes. Our findings are consistent with numerical simulations which have shown that cold dense clumps in galactic outflows can be compressed by ram pressure, and also progressively ablated and stripped before complete disintegration. We have shown that some clumps could survive their passage along a galactic outflow. These are advected into the circumgalactic environment, where their remnants would seed condensation of the circumgalactic medium to form new clumps. The infall of these new clumps back into the galaxy and their subsequent re-entrainment into the galactic outflow form a loop process of galactic material recycling.

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“…In addition, the halo has been observed in other interstellar medium components, for example in X-ray emitting gas (Wang et al 2001;Yamasaki et al 2009), dust (Martin & Kern 2001;Neininger & Dumke 1999), and molecular gas (Rand 2000;Irwin et al 2011). The central region has an interesting structure consisting of three collinear emission peaks (Ekers & Sancisi 1977;Duric et al 1982;Golla 1999).…”

Section: Introductionmentioning

confidence: 99%

Magnetic field structure and halo in NGC 4631

Mora

Krause

2013

A&A

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Context. All of the edge-on spiral galaxies observed so far present a similar magnetic field configuration, which consists of a planeparallel field in the disk and an X-shaped field at larger z-distances from the plane of the galaxy. Only NGC 4631 seems to have a different field orientation in its disk. Along the eastern and western halves of the disk of NGC 4631 the magnetic field orientation is parallel to the galactic plane, but in the central region of the disk a vertical field seems to dominate. Aims. In order to clarify whether NGC 4631 has a unique magnetic field configuration in the central region along its disk, we present high-resolution Faraday-corrected polarization data. Methods. Radio continuum observations of NGC 4631 at 4.85 GHz were performed with the VLA. In addition, observations were made with the Effelsberg telescope at 4.85 GHz and at 8.35 GHz. These were analyzed together with archival VLA-data at 8.35 GHz. The single-dish and interferometer data were combined to recover the missing zero-spacings. Results. We determined an integrated total spectral index of α tot = −0.78 ± 0.04 and a nonthermal integrated spectral index of α nth = −0.87 ± 0.03. The vertical scale heights in NGC 4631 vary significantly in different regions within the galaxy and their mean values at 4.85 GHz are with 2.3 kpc (370 pc) for the thick (thin) disk higher than the mean values found so far in six other edge-on spiral galaxies. This may originate in the tidal interaction of NGC 4631 with its neighbouring galaxies. The rotation measures are characterized by a smooth large-scale distribution. Along the galactic plane the degree of Faraday depolarization is significantly high. We estimated a total magnetic field strength in the disk of NGC 4631 of B t ≈ 9 ± 2 μG and an ordered field strength of B ord ≈ 2 ± 1 μG. The total field strengths in the halo are of the order of the total magnetic field strength in the disk, whereas the ordered field strengths in the halo seem to be higher than the value in the disk. Conclusions. The derived distribution of rotation measures implies that NGC 4631 has a large-scale regular magnetic field configuration. Despite the strong Faraday depolarization along the galactic plane and the strong beam depolarization in the transition zone between the disk and halo, our research strongly indicates that the magnetic field orientation along the central 5-7 kpc of the disk is also plane-parallel. Therefore, we claim that NGC 4631 also has a magnetic field structure plane-parallel along its entire disk, similar to all other edge-on galaxies observed up to now.

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X-Ray Halo around the Spiral Galaxy NGC 4631 Observed with Suzaku

Cited by 47 publications

References 38 publications

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

X-Ray and Gamma-Ray Observations of the Fermi Bubbles and NPS/Loop I Structures

Charge-exchange emission and cold clumps in multiphase galactic outflows

Magnetic field structure and halo in NGC 4631

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